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What caused a regime shift in the Wabash River? Indiana AFS Feb 28, 2014. Mark Pyron, Jesse Becker, Dawn DeColibus, Kevin Wyatt, and Allison Rober Center of Aquatic Biology and Fisheries Environmental Science. Previous results: regime shift. Regress body size on size bins - PowerPoint PPT Presentation
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What caused a regime shift in the Wabash River?
Indiana AFSFeb 28, 2014
Mark Pyron, Jesse Becker, Dawn DeColibus, Kevin Wyatt, and Allison Rober
Center of Aquatic Biology and FisheriesEnvironmental Science
Previous results: regime shift• Regress body size on size bins
• Negative slope = inefficient transfer
Wabash River Regime Shift• Body size distribution of fishes changed:
1974-2008
Abundances in trophic groups
Potential causes of regime shift?
• Large flood / severe drought
• Point-source pollution
• Over-harvesting fish
• Excess nutrients, increased algae, diet change in upper trophic levels
Diet of fishes change?Pilot analysis
• Isotope analyses: 13C and 15N ratiosMuseum archives 1960-2008
Predator = spotted bass, drum, sucker
Omnivores = spotfin shiner
Detritivore = gizzard shad
One trophic level ~ 3 ppt d15N
http://sofia.usgs.gov
Algae Macrophytes
INHS archival fishes: Wabash River
• Gizzard shad now consume additional sources
NANFA.ORG
• Gizzard shad consume additional sources• Shiner consume lower trophic sources
NANFA.ORG
Upstream individuals consume at lower trophic levels
ISOTOPE RESULTS
• Change in diet of consumer fishes (planktivore / omnivore) in 1990s
• Different algae? • Different nutrients?• Impact of Asian carp?
STOMACH CONTENTS GIZZARD SHAD
• Has diet changed?
Summary
• Fish diets changed 1960-2000
• Gizzard shad consume less algae, low quality
• Algal assemblage changed – cause?
SummarySummary
• Fish diet changedFish diet changed• Algal assemblage changedAlgal assemblage changed• Asian carp / Higher nutrients?Asian carp / Higher nutrients?